Overspeed prevention system for elevator cars

ABSTRACT

An overspeed prevention system for elevator cars is disclosed which is especially adapted for elevators of the type used in material handling systems. Speed responsive means in the form of an electrical generator is provided on the elevator car and produces an output voltage of one polarity exceeding a predetermined magnitude in response to overspeed in the upward direction and produces an output voltage of the opposite polarity and exceeding a predetermined magnitude in response to overspeed in the downward direction. A first polarity responsive switching means is effective to de-energize the elevator motor in a regulated manner in response to upward overspeed. A second polarity responsive switching means responds to the downward overspeed voltage and initiates the application of brake means to stop the elevator car. The brake means includes a pair of brakes which utilize an actuator including one or more pair of brakes which utilize an actuator including one or more pyrotechnic charges which are provided with electrical detonators. The switching means are effective to connect the generator to the detonator circuit for the pyrotechnic charges and, to ensure firing thereof, pulsing means are interposed to provide repetitive firing impulses across the detonator circuit.

llnited States Patent i191 Snyder 1*Mar. 25, 1975 [75] Inventor: James H. Snyder, Battle Creek,

Mich.

[73] Assignee: Clark Equipment Company,

Buchanan, Mich.

[ Notice: The portion of the term of this patent subsequent to Aug. 23, 1988, has been disclaimed.

[22] Filed: June 15, 1970 [21] Appl. No.: 46,236

[51] Int. Cl. B66b 5/06 [58] Field of Search 187/80, 83, 86, 90, 93,

[56] References Cited UNITED STATES PATENTS 324,751 8/1885 Curtiss 187/80 767,930 8/1904 Eskilsson 187/39 2,489,984 11/1949 Shoemaker.... 294/831 ER 2,511,697 6/1950 Clift 187/90 OVERSPEED PREVENTION SYSTEM FOR ELEVATOR CARS Primary Examiner-Evon C. Blunk Assistant Examiner-James L. Rowland Attorney, Agent, or Firm-Harry G. Thibault [5 7] ABSTRACT An overspeed prevention system for elevator cars is disclosed which is especially adapted for elevators of the type used in material handling systems. Speed responsive means in the form of an electrical generator is provided on the elevator car and produces an output voltage of one polarity exceeding a predetermined magnitude in response to overspeed in the upward direction and produces an output voltage of the opposite polarity and exceeding a predetermined magni tude in response to overspeed in the downward direction. A first polarity responsive switching means is ef fective to de-energize the elevator motor in a regulated manner in response to upward overspeed. A second polarity responsive switching means responds to the downward overspeed voltage and initiates the application of brake means to stop the elevator car. The

, brake means includes a pair 'of brakes which utilize an actuator including one or more pair of brakes which utilize an actuator including one or more pyrotechnic charges which are provided with electrical detonators The switching means are effective to connect the generator to the detonator circuit for the pyrotechnic charges and, to ensure firing thereof, pulsing means are interposed to provide repetitive firing impulses across the detonator circuit.

17 Claims, 5 Drawing Figures PATENTEDHARZSISYS sum 1 n; 2

zgyder ATTORNFYS INVENfUR James 5 OVERSPEED PREVENTION SYSTEM FOR ELEVATOR CARS This invention relates to elevators and, more particularly, to an overspeed prevention system especially adapted for material handling or cargo elevators.

In automatic storage or warehouse systems a material handling vehicle is movable in an aisle between an array of storage bins to preselected stations for deposit or withdrawal of material units. Such a vehicle, commonly referred to as a stacker vehicle, includes a mast or frame and an elevator car movable therein foraccess to the storage bins at different elevations. Such systems are designed to operate at high speed and it is desired to minimize the travel time between stations for the stacker vehicle and minimize the travel time between bins for the elevator. For this purpose the elevator car is driven upwardly or downwardly, depending upon the destination, simultaneously with the stacker vehicle travel between stations. While the elevator car is adapted for high-speed operation and is operated in a substantially unattended manner, excessive speeds in either the upward or downward direction constitute a source of danger to personnel who may be in the vicin ity as well as to the equipment and the materials being handled. Excessive speed in the downward direction may result from a variety of causes such as a failure in the control system or breakage of the lift chain which may, ofcourse, result in uncontrolled overspeed. In any case of excessive downward speed of the elevator car it is desired to bring the car to a stop as soon as possible by the application ofbrakes. Excessive speed of the elevator car in the upward direction is most likely to result from a failure in the control system of a governor or tachometer generator. Overspeed in the upward direction may be prevented by interruption of'the driving power to the elevator car but, of course, provision must be made to maintain the car in position or in upward motion within the desired operating speed.

It has been a common practice to provide material handling elevators of various types with safety brakes in the event of mechanical failure, such as cable breakage. In such elevators the safety brakes are commonly spring actuated and self-energizing and the application thereof is initiated by an arrangement for detecting a slack cable at the elevator car. In passenger elevators safety brake systems are also employed and commonly utilize an overspeed governor driven by a governor cable or the like to sense car speed. When an overspeed condition is reached in either the upward or downward direction the governor is effective to cause actuation of a brake in' the drive train of the elevator motor. Such an elevator may also include additional brake means carried on the car which are adapted to grip the elevator guide rails in the event of a failure of the lift cable or downward speed of the car such that the car is disengaged from the governor cable.

In accordance with this invention there is provided an overspeed prevention system for an elevator car for both upward and downward travel of the car which is operable independently of the lift cable and mechanical connection with the drive train of the elevator car. The system requires no external source of energization and it may be carried entirely on the elevator car. This is accomplished by means of an electrical generator operatively connected between the elevator car and frame for developing a voltage having a magnitude corresponding to the speed of the car and having a polarity corresponding to the direction of travel. A first unidirectionally conductive voltage responsive switching means is connected with the generator and is adapted to connect it to the electrical initiator for brake means on the elevator car in response to an excessive downward speed. A second unidirectionally conductive voltage responsive switching means is connected with the generator and is adapted to effect a regulated deenergization of the driving motor for the elevator car in response to excessive speed in the upward direction of the elevator car.

Also, in accordance with the invention, the overspeed brake control system is independent of spring ac tuators and the application of the brakes is electrically controlled. This is accomplished by the provision of brake means with a pyrotechnic actuator having an electrical initiator or detonator. Thus, the connection of the generator by the switching means to the detonator provides instantaneous application of the brake means. Such an arrangement may be extremely compact and yet have a powerfulbrake actuator. Reliability of operation is assured by provision of plural pyrotechnic charges in-each brake actuator. Each pyrotechnic charge is provided with its own electrical detonator and impulse means is electrically connected between the switching means and the detonators to deliver successive electrical pulses at a high rate to insure the firing of each detonator.

Further in accordance with the invention, there is provided an elevator brake for use in an overspeed control system which may be mounted on the elevator car for coaction with reaction means on the elevator frame and having an entirely self-contained actuator, i.e.,

' without the need for any mechanical linkage for the initiation of brake application by the actuator. This is accomplished by use of an actuator which is energized by a pyrotechnic charge having an electrical detonator and thus requiring only an electrical connection for initiating the brake application. Further, the brake application is produced by a direct and rigid drive means interconnecting the brake shoes with the actuator piston driven by the pyrotechnic charge. This direct mechanical drive assures positive brake engagement through a wedge or cam displacement mechanism which serves to apply the explosive power of the pyrotechnic charge in a controlled manner to urge the brake shoes into engagement with the reaction member. In this manner the entire brake is self-contained in exceedingly small volume and may be disposed on the elevator car within the channel-shaped guide track with serves as the brake reaction member.

A more complete understanding of this invention may be obtained from the detailed description which follows taken with the accompanying drawings in which:

FIG. 1 is a perspective view of an elevator including the overspeed brake control system of this invention;

FIG. 2 is a view in elevation of the brake in the disengaged condition;

FIG. 3 is an elevation view showing the brake shoes in engaged condition;

FIG. 4 is a sectional view of the brake taken on lines 4-4 of FIG. 2 and showing the pyrotechnic actuator of the brake; and

FIG. 5 is a schematic diagram showing the overspeed prevention system for both upward and downward travel of the elevator car.

Referring now to the drawings, there is shown an illustrative embodiment of the invention in an overspeed prevention system for an elevator of the type which is especially adapted for use in a stacker vehicle in an automatic warehouse system. As such, the elevator is adapted for high speed operation under automatic control in a substantially unattended manner. The overspeed prevention system is adapted to respond automatically in an instantaneous and positive manner to an overspeed condition in either the upward or downward direction of the elevator car.

Referring now to FIG. 1, there is illustrated an elevator including a car movable vertically within an elevator frame including guide tracks 12 and 14 of channel configuration at opposite sides of the car. Lift means for the car includes a drive chain 16 which is drivably connected through a drive train to an electric motor, not shown in FIG. 1.

The overspeed prevention system of this invention includes an electrical speed sensing means in the form of an electrical generator 18 mounted by its stator on the car 10. The rotor of the generator is provided with a pinion gear 20 on its shaft and meshing with a rack gear 22 on the flange of the guide track 12. By' the engagement of the pinion gear 20 with the rack gear 22 the rotor of the generator 18 is driven at a speed and in a direction which corresponds to the vertical speed and direction of the elevator car 10. The generator 18 is preferably a direct current generator with a permanent magnet field and produces an output voltage magnitude corresponding to the speed of rotation with a polarity corresponding tothe direction of rotation. It is desirable to use a DC generator which exhibits a substantially linear variation in output voltage as a function of rotational speed over the range of speeds to be encountered in the overspeed prevention system. The generator may advantageously employ a permanent magnet rotor and a stator winding having a rectifier connected therewith, thus avoiding the use of a commutator or brushes and slip rings.

To provide for emergency braking of the elevator car in the downward direction of travel, the elevator is provided with brake means adaptedupon actuation to bring the car 10 to a stop relative to the frame of the elevator. For this purpose the brake means includes a brake 24 on one side of the car and a brake 26 on the other side of the car. The brakes 24 and 26 are identical to each other and are mounted at opposite ends of a support beam 28 which extends beneath the floor of the car 10 and is adapted to support the same during emergency braking. As shown in FIGS. 1 and 2, the brake 24 is disposed within the channel configuration of the guide track 12 with suitable clearance from the guide track and similarly the brake 26 is disposed within the channel of guide track 14.

Referring now to FIGS. 2 and 4, the structure of the brake 24 will be described, it being understood that brake 26 is of identical construction. Thebrake 24 comprises a body 30 suitably in the form of a rectangular block which is mounted on the end of the support beam 28 and secured thereto by bolts not shown. A pair of rotatable dogs or brake shoes 32 and 34 are mounted for rotation on the body 30 by a pair of headed studs 36 and 38, respectively, which are suitably press fitted or otherwise fixedly secured in the body 30. The brake shoes 32 and 34 are disposed sideby-side with the pivot axis thereof spaced equidistantly from the centerline of the body 30. The brake shoe 32 is of a generally cylindrical configuration having a flat outer surface 40' and formed with a generally radial protrusion or keeper arm 42 extending transversely of the body 30. It is noted that the keeper arm is of lesser thickness than the body of the shoe 32 and has a front surface recessed therefrom which defines a shoulder 44. The brake shoe 32 is provided with a serrated radial surface 46 extending between the flat surface 40 and the keeper arm 42 to provide a non-skid or biting engagement with the guide track 12 which constitutes the brake reaction member when the brakes are engaged. To provide for angular displacement of the brake shoe 32 to cause brake engagement, it is provided with a flat camming surface or shoulder 48 on the rearward face thereof and extending obliquely of the centerline of the brake body 30.

Brake shoe 34 is of a construction similar to that of brake shoe 32 and also comprises a generally cylindri' cal body with a flat outer surface 50 and a keeper arm 52. The brake shoes 32 and 34 are adapted for rolling contact with each other at the circular portions of their peripheral edges. It is noted that the keeper arm 52 is of lesser thickness than the body portion of the brake shoe 34 and has a front surface flush with that of the body portion but has a back surface which is recessed relative to that of the body portion, thereby providing a shoulder 54. Thus, the keeper arm 52 is adapted to overlie the keeper arm 42 with the side thereof in abutment with the shoulder 44 and the side of the keeper arm 42 in abutment with the shoulder 54. The brake shoe 34 is provided with a serrated radial surface 56 which extends between the flat surface 50 and the keeper arm 52 to provide for non-skid or biting engagement withthe other side of the guide track 12 when the brake is engaged. The brake shoe 34 is also provided with a flat camming surface 58 which extends obliquely of the centerline of the brake body 30.

The brake 24 is provided with an actuator which comprises a slide bar 62, a piston 64 secured thereto and pyrotechnic charges 66 and 68 disposed in a support block 70. The slide bar 62 is mounted on the brake body 30 for reciprocable motion thereon within an axially extending rectangular groove 72 formed in the body 30 and extending throughout the length of the body. The slide bar is of reduced thickness at its lower end and is formed at an intermediate portion with a cam 74 having one side aligned with the camming surface 48 of the brake shoe 32 and having its other side aligned with the camming surface 58 of the brake shoe 34. The slide bar 62 is also provided with a stop pin 76 adjacent its lower end in engagement with the lower edges of the keeper arms 42 and 52 of the brake shoes 32 and 34, respectively.

The piston 64 is of cylindrical cup-shape configuration and is fixedly secured, as by welding of the skirt thereof, to the back side of the slide block 62. The piston 64 is slidably disposed within a cylindrical bore 78 in the body 30 which has a continuous circumferential wall except for an opening into the bottom of the rectangular groove.72. This interconnection of the groove 72 and the bore 78 permits the slide bar 62 and the piston 64 to be connected together and to move reciprocably in the brake body 30. The piston 64 and hence the slide block 62 are resiliently biased in the upward position, as illustrated in FIG. 4, by a helical spring 80 disposed in the lower portion of the bore 78.

The support block 70 is a generally cylindrical body with a mounting flange 82 bolted to the body and provided with a slot or groove 84 to accommodate the slide bar 62. The support block 70 includes a cylindrical body portion extending into the piston skirt and includes a pair of axially extending chambers 86 and 88 adapted to receive the pyrotechnic charges 66 and 68, respectively. The pyrotechnic charges are of conventional design and each includes a closed cylinder containing pyrotechnic material and an electrical detonator, the cylinder being formed with a bellows portion to permit axial extension of the cylinder when the pyrotechnic material is exploded. Additionally, the brake 24 is provided with a switch 90 of conventional type including a plunger actuator which engages the back side of the slide bar 62 when the bar and the piston 64 are in the uppermost position. The switch 90 is provided with contacts which are closed with the plunger in the retracted position, as shown in FIG. 4, and which are opened when the plunger is in the extended position resulting from downward motion of the slide bar 62.

The brake 24, as shown in FIGS. 2 and 4, is in the disengaged position and thus it is movable vertically within the guide track 12 with ample clearance between the brake shoes 32 and 34 and the channel flanges of the guide track 12. The brake shoes 32 and 34 are retained in this position by the engagement of the keeper arms 42 and 52 with the stop pin 76 which in turn is supported by the slide bar 62. Slide bar 62 is retained in its uppermost position by the bias spring 80 which engages the piston 64 and urges it along with the slide bar 62 to the uppermost position. When either of the pyrotechnic charges 66 or 68 is detonated, the expansion thereof forces the piston 64 downwardly in the bore 78 and carries therewith the slide bar 62. Thus, the stop pin 76 is moved downwardly away from the keeper arms 42 and 52 and the cam 74 engages the camming surfaces 48 and 58 on the brake shoes 32 and 34, respectively, causing them to rotate clockwise and counterclockwise, respectively. As shown in FIG. 3, such rotation causes the serrated surfaces 46 and 56 to move laterally outwardly into engagement with the channel flanges of the guide track 12. Thus, the serrated surfaces 46 and 56 will bite into the metal of the guide track 12 and in a self-energizing manner the downward thrust of the elevator car 10 will tend to cause additional rotation of the brake shoes 32 and 34 thereby increasing the engagement force thereof with the guide track. The brake 26, which is identical in construction to brake 24, will operate in the same manner simultaneously and bring the elevator car 10 to a stop over a very short distance of travel.

The overspeed prevention system of this invention is provided with a control circuit which will be described with reference to FIG. 5. The control system comprises, in general, the generator 18 and a first switching means 92 responsive to overspeed of the car in the upward direction to de-energize the driving motor 94 for the elevator car; it also includes a second switching means 96 responsive to overspeed of the car in the downward direction to energize a detonator circuit 98 for the pyrotechnic charges through a pulsing circuit 100. The generator 18 develops an output voltage with the polarity indicated in FIG. 5 when the car is moving downwardly and-with the opposite polarity when it is moving upwardly.

Considering the control circuit in greater detail, the permanent magnet generator 18 has its output terminals connected across the first switching means 92 which includes, in series connection, a rectifier or unidirectionally conductive device 1.02, a current limiting resistor 104 and the energizing coil of a voltage sensitive relay 106. The rectifier device 102 is poled to conduct when the generator voltage has a polarity corresponding to upward motion. The: relay 106 includes a switching means or contacts 108 adapted to open the energizing circuit of the drive motor 94 when the relay 106 is actuated or pulled in. The energizing circuit for the drive motor 94 also includes the contacts of the switch which, as described above, are opened when the brake 24 is applied.

The switching means 96 is also connected across the output terminals ofthe generator 18 and includes a rectifier or unidirectionally conductive device 110 which is poled to conduct in the forward direction when the generator 18 produces a voltage in response to the downward motion of the elevator car 10. The rectifier device 110 is serially connected with a current limiting resistor 112 and the energizing coil of a voltage sensitive relay 114. The relay 114 includes a pair of normally open switch contacts 116 which are closed when the relay 114 is actuated or pulled in. The switch contacts 116 are adapted to connect the generator 18 across the detonator circuit 98 in response to overspeed of the elevator in the downward direction. A capacitor 118 is connected across the contacts 116 for protection thereof against the inductive surge current occurring in operation of the circuit.

In order to connect the detonator circuit 98 withthe generator 18, a transformer 120 is provided with its primary winding connected across the generator 18' through the rectifier device 110 and the switch contacts 116. The secondary winding of the transformer 120 has one terminal connected to the adjacent terminal of the primary winding in autotransformer fashion. The detonator circuit 98 is connected across the secondary winding and includes detonators 122 and 124 of the pyrotechnic charges 66 and 68 in brake 24 and also includes parallel connected detonators 126 and 128 of the pyrotechnic charges in the brake 26. A pair of load resistors 130 and 132 are also connected in parallel across the secondary winding of the transformer 120. The transformer provides a suitable transformation ratio to deliver the required current to the detonators. The transformer 120' and the switching means 96 function as a pulsing circuit for energization of the detonator circuit 98 in a manner to be described.

In operation of the inventive overspeed prevention system, the control system of FIG. 5 responds to overspeed in either direction of the elevator car. Assuming that the car is moving upwardly within the rated speed, the generator 18 will be driven thereby and will produce a voltage across the switching means 92 causing conduction in the forward direction through the rectifier device 102. However, the voltage will be below the threshold value for the relay 106 and the resultant current is insufficient to cause actuation thereof. Under these conditions, the voltage of generator 18 is applied across the switching means 96 and the rectifier device 110 therein in the nonconductive: direction and, accordingly, current flow through the relay 114 is blocked. If the speed of the elevator car 10 in the upward direction should increase beyond the rated speed the voltage developed by the generator 18 will be increased correspondingly. Accordingly, the voltage across the switching means 92 will be increased and the relay 106 will be actuated. This will open the switch contacts 108 in the energizing circuit of the drive motor 94 thus reducing the speed of the elevator car. As soon as the speed is reduced below the rated value the voltage developed by the generator 18 will be decreased correspondingly and the relay 106 will drop out allowing the contacts 108 to reclose and restore the energization to the motor 94. In such a manner by repetitive actuation of the relay 106 the speed of the elevator car in the upward direction will be regulated at a value within the rated speed.

When the elevator car 10 is travelling in the downward direction the generator 18 is driven thereby and develops an output voltage across the switching means 92 and the switching means 96. The polarity of the generator voltage across the switching means 92 is in the non-conductive direction. However, the polarity of the generator voltage'across the rectifier device 110 in switching means 96 is in the forward direction. When the downward speed of the elevator car is within the rated speed, the voltage across the relay 114 is below the threshold value and the current flow therethrough is insufficient to pull in the relay. However, when the speed of the car exceeds the rated value, the relay 114 is pulled in and the contacts 116 are closed. Accordingly, the output voltage of the generator 18 is applied across the primary winding of the transformer 120 through the rectifier device 110 and the contacts 116. This causes a transient primary current in the transformer 120 which induces a voltage across the secondary winding and the detonator circuit 98. Accordingly, the detonators 122, 124, 126 and 128 are energized by the resultant current flow and the respective pyrotechnic charges in the brakes 24 and 26 are exploded thereby. The brakes 24 and 26 are applied in the manner previously described and the elevator car 10 is brought to a stop. A single pyrotechnic charge in each brake is effective when fired to apply the brake and two charges are used in each brake only for the purpose of back-up in the case of a failure of one pyrotechnic charge. The pulsing circuit 100 is provided to make sure that the detonators of both the first and second charges in each brake are fired when the overspeed condition occurs.

When the DC voltage of the generator 18 is applied across the primary winding of the transformer 120 the transient current therein is initially limited by the reactive impedance and will increase toward a final value which is limited by the resistance of the circuit. This transient current causes a voltage to be induced across the secondary winding and a current impulse in the detonator circuit 98 to energize the detonators. However, as the rate of change of magnetizing flux in the transformer decreases, the current increases toward its final value thus decreasing the voltage drop across the inductive reactance of the transformer primary winding. The voltage drop is correspondingly increased across the resistance of the circuit, including the internal resistance of the generator. The transformer 120 is desirably adapted to be driven into magnetic saturation by the magnetizing current thus causing an abrupt decrease in the flux rate of change and the current im- 8 pulse rise time. The resulting large surge current, in effect, loads down the generator and the terminal voltage decreases so that the voltage across the relay 114 drops below the threshold value and the contacts 116 are opened. Interruption of the current in the primary winding causes the magnetic flux field to collapse and induce a voltage of reverse polarity across the secondary winding. As a result, a second current impulse is delivered to the detonator circuit 98 to fire any detonators which were not fired by the first impulse. Thus, a limit cycle occurs in the operation of the switching means 96 and the transformer 120. With the relay contacts 116 open, the generator voltage will increase again if the overspeed condition persists until the voltage across relay 114 exceeds the threshold value and the cycle described above is repeated. Consequently, the pulsing circuit operates to apply repeated firing impulses to the detonator circuit to ensure that the detonators are fired to bring the elevator car to a stop. When the brake 24 is applied by firing one of the charges and the slide bar 62 is displaced downwardly thereby, the switch is actuated and the contacts thereof are open to interrupt the energizing circuit of the drive motor 94.

Although the description of this invention has been given with respect to a particular embodiment, it is not to be construed in a limiting sense. Many variations and modifications will now occur to those skilled in the art. For a definition of the invention reference is made to the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An overspeed brake control system for an elevator comprising: an electrical generator adapted to be oper-' atively connected with an elevator car to generate a voltage corresponding to the speed of the car, brake means for said car including a pyrotechnic actuator therefor with an electrical detonator, and voltage responsive switching means connected with the generator and adapted to connect said generator with said electrical detonator when the voltage of the generator reaches a predetermined value upon the occurrence of transformer having a primary winding connectable across said generator through said switching contacts and a secondary winding connected across said electrical detonator, the transformer primary being con-,

nected across the generator when said switching contacts are closed to produce a first voltage impulse across said detonator, the core of said transformer being driven into magnetic saturation by the generator current thereby producing a voltage across said relay below said predetermined value whereby the switching contacts open and interrupt the primary current in said transformer and thereby produce a second voltage impulse across the detonator.

5. The invention as defined in claim 1 including a pulse producing means connected between said generator and said detonator whereby repeated pulses are applied to the detonator while the speed of the car is excessive.

6. The invention as defined in claim 5 wherein the pulse producing means includes said switching means and reactive impedance adapted to impose a time varying load on said generator so that the voltage thereof varies above and below said predetermined value when the speed is excessive.

7. The invention as defined in claim 5 wherein said pyrotechnic actuator includes plural pyrotechnic charges each having an electrical detonator, all of said detonators being connected in parallel to said pulse producing means whereby the detonators are subjected to repeated voltage pulses to insure that each pyrotechnic charge is fired in response to an overspeed condition.

8. The invention as defined in claim 7 wherein said brake means is provided with electrical switching means operatively connected with said actuator and electrically connected with the drive means for said elevator car and being adaptd to interrupt said drive means when said brake means is actuated by the pyrotechnic actuator.

9. The invention as defined in claim 1 wherein said brake means comprises a brake shoe and operating member connected with said actuator and engageable with said brake shoe for displacing the same to cause energization of said brake means to stop said elevator car.

10. An overspeed prevention system for an elevator comprising: an elevator car movable relative to a frame by a drive motor and comprising a direct current electrical generator operatively connected between the car and the frame and adapted to generate a voltage corresponding to the speed of the elevator car, brake means for said car including an electrically energized actuator therefor. a first unidirectionally conductive voltage responsive switching means connected with the generator and responsive to a predetermined voltage of one polarity for connecting said generator across said electrical energizing means to cause said brake means to be actuated when said elevator car is moving downwardly at an excess speed and second unidirectionally conductive voltage responsive switching means connected with said generator and responsive to a predetermined voltage of the other polarity for de-energizing said drive motor when said elevator car is moving upwardly at an excessive speed.

11. The invention as defined in claim 10 wherein said actuator includes a pyrotechnic charge with an electrical detonator.

12. An overspeed prevention system for an elevator car movable relative to a frame by a driving motor and comprising a direct current generator operatively con nected between the elevator car and the frame and adapted to generate a voltage corresponding to the speed of the car, brake means for said our including at least one brake shoe, a pyrotechnic actuator therefor with an electrical detonator, switching means for deenergizing said driving motor, first unidirectionally conductive voltage responsive means connected with said generator and adapted to connect said generator across said electrical detonator when the voltage of the generator reaches a predetermined value and is ofa polarity corresponding to downward motion of said car, and second unidirectionally conductive voltage responsive means connected with said generator and adapted to actuate said switching means for de-energizing said driving motor when the voltage of said generator reaches a predetermined value and is of a polarity corresponding to upward motion of said car.

13. An overspeed brake control system for an elevator comprising: an elevator car movable relative to a frame, brake means for said car including a pyrotechnic actuator therefor with an electrical detonator, a source of voltage on said car, control means responsive to the speed of said elevator car for connecting the voltage source to the electrical detonator, said brake means comprising at least one brake shoe, and an operating member connected with the actuator and engage able with the brake shoe for displacing it into engagement with the brake reaction member.

14. The invention as defined in claim 13 wherein said voltage source is a direct current generator operatively connected between the elevator car and the frame.

15. The invention as defined in claim 14 wherein said control means is a voltage responsive switching means connected with the generator and adapted to connect the generator to the electrical detonator when the voltage of the generator reaches a predetermined value.

16. The invention as defined in claim 15 including a pulse producing means connected between the generator and the detonator. 7

17. The invention as defined in claim 16 wherein said brake means includes first and second brakes, each including an actuator with plural pyrotechnic charges, each of said charges having an electrical detonator, said detonators being connected in parallel to said pulse producing means whereby the detonators are subjected to repeated voltage pulses to insure that each pyrotechnic charge is fired in response to an overspeed 

1. An overspeed brake control system for an elevator comprising: an electrical generator adapted to be operatively connected With an elevator car to generate a voltage corresponding to the speed of the car, brake means for said car including a pyrotechnic actuator therefor with an electrical detonator, and voltage responsive switching means connected with the generator and adapted to connect said generator with said electrical detonator when the voltage of the generator reaches a predetermined value upon the occurrence of excessive speed of said car.
 2. The invention as defined in claim 1 wherein said generator is a direct current generator and said voltage responsive switching means is connected thereto through a unidirectionally conductive device so that said switching means is responsive only to the generator voltage corresponding to downward motion of the elevator car.
 3. The invention as defined in claim 2 wherein said voltage responsive switching means comprises a voltage sensitive relay including an energizing coil and switching contacts connected in parallel therewith to said detonator.
 4. The invention as defined in claim 3 including a transformer having a primary winding connectable across said generator through said switching contacts and a secondary winding connected across said electrical detonator, the transformer primary being connected across the generator when said switching contacts are closed to produce a first voltage impulse across said detonator, the core of said transformer being driven into magnetic saturation by the generator current thereby producing a voltage across said relay below said predetermined value whereby the switching contacts open and interrupt the primary current in said transformer and thereby produce a second voltage impulse across the detonator.
 5. The invention as defined in claim 1 including a pulse producing means connected between said generator and said detonator whereby repeated pulses are applied to the detonator while the speed of the car is excessive.
 6. The invention as defined in claim 5 wherein the pulse producing means includes said switching means and reactive impedance adapted to impose a time varying load on said generator so that the voltage thereof varies above and below said predetermined value when the speed is excessive.
 7. The invention as defined in claim 5 wherein said pyrotechnic actuator includes plural pyrotechnic charges each having an electrical detonator, all of said detonators being connected in parallel to said pulse producing means whereby the detonators are subjected to repeated voltage pulses to insure that each pyrotechnic charge is fired in response to an overspeed condition.
 8. The invention as defined in claim 7 wherein said brake means is provided with electrical switching means operatively connected with said actuator and electrically connected with the drive means for said elevator car and being adaptd to interrupt said drive means when said brake means is actuated by the pyrotechnic actuator.
 9. The invention as defined in claim 1 wherein said brake means comprises a brake shoe and operating member connected with said actuator and engageable with said brake shoe for displacing the same to cause energization of said brake means to stop said elevator car.
 10. An overspeed prevention system for an elevator comprising: an elevator car movable relative to a frame by a drive motor and comprising a direct current electrical generator operatively connected between the car and the frame and adapted to generate a voltage corresponding to the speed of the elevator car, brake means for said car including an electrically energized actuator therefor, a first unidirectionally conductive voltage responsive switching means connected with the generator and responsive to a predetermined voltage of one polarity for connecting said generator across said electrical energizing means to cause said brake means to be actuated when said elevator car is moving downwardly at an excess speed and second unidirectionally conductive voltage responsive switching means connected with said generator and responsive to a predetermIned voltage of the other polarity for de-energizing said drive motor when said elevator car is moving upwardly at an excessive speed.
 11. The invention as defined in claim 10 wherein said actuator includes a pyrotechnic charge with an electrical detonator.
 12. An overspeed prevention system for an elevator car movable relative to a frame by a driving motor and comprising a direct current generator operatively connected between the elevator car and the frame and adapted to generate a voltage corresponding to the speed of the car, brake means for said car including at least one brake shoe, a pyrotechnic actuator therefor with an electrical detonator, switching means for de-energizing said driving motor, first unidirectionally conductive voltage responsive means connected with said generator and adapted to connect said generator across said electrical detonator when the voltage of the generator reaches a predetermined value and is of a polarity corresponding to downward motion of said car, and second unidirectionally conductive voltage responsive means connected with said generator and adapted to actuate said switching means for de-energizing said driving motor when the voltage of said generator reaches a predetermined value and is of a polarity corresponding to upward motion of said car.
 13. An overspeed brake control system for an elevator comprising: an elevator car movable relative to a frame, brake means for said car including a pyrotechnic actuator therefor with an electrical detonator, a source of voltage on said car, control means responsive to the speed of said elevator car for connecting the voltage source to the electrical detonator, said brake means comprising at least one brake shoe, and an operating member connected with the actuator and engageable with the brake shoe for displacing it into engagement with the brake reaction member.
 14. The invention as defined in claim 13 wherein said voltage source is a direct current generator operatively connected between the elevator car and the frame.
 15. The invention as defined in claim 14 wherein said control means is a voltage responsive switching means connected with the generator and adapted to connect the generator to the electrical detonator when the voltage of the generator reaches a predetermined value.
 16. The invention as defined in claim 15 including a pulse producing means connected between the generator and the detonator.
 17. The invention as defined in claim 16 wherein said brake means includes first and second brakes, each including an actuator with plural pyrotechnic charges, each of said charges having an electrical detonator, said detonators being connected in parallel to said pulse producing means whereby the detonators are subjected to repeated voltage pulses to insure that each pyrotechnic charge is fired in response to an overspeed condition. 